1. Field of the Invention
This invention relates to vangs.
To maintain the leech of the mainsail of a yacht under a tension suited to the current angle of attack of the yacht, the wind speed and direction, and other variables affecting the sailing performance of the yacht, and, in particular, to provide, in the mainsail, an approximation, at all times, to an optimum aerodynamic shape, resort is had, to the action of tensioning force applied to the main-boom by the main-sheet, in conjunction with a topping lift fitted to the vessel. Commonly, in the case of yachts, the main-sheet comprises a multi-sheave block and tackle system.
To enable the tension in the leech of the mainsail to be maintained reasonably constant, even when sailing conditions demand a change of angle, in azimuth, of the main-boom with respect to the fore and aft direction of the vessel, in adjusting to variation in wind strength or direction, or when changing tack, the main-sheet block and tackle system is connected to a principal part, the carriage, of a device referred to as a "traveller", the other principal part of which is a track extending athwartships, across the deck of the yacht, at a position between the main mast and the transom of the vessel.
Whilst the main-sheet block and tackle system is effective in holding the main-boom down under a desired tension at any azimuthal position of the boom within the range permitted by the traveller, in order to achieve azimuthal positions for the main-boom beyond the extremities of the traveller, the main-sheet must be slackened-off. Under the resulting loss of tension in the main-sheet, tension in the main-sail, particularly at the leech thereof, compels the main-boom to swing upwardly, the main-sail departing in shape from a desired relatively flat aerodynamic form to a significantly rounder shape, inferior, from an aerodynamic view-point, from the flatter shape to which tension in the main-sheet contributes.
To counter this, and to enable the main-boom to adopt positions beyond the range of the traveller, it is a common practice to employ what is referred to as a kicking strap, or vang, in the control of the pitch and azimuth angles of the main-boom, with respect to the main-mast.
2. Description of the Prior Art
In its most basic form, the vang of the prior art comprises a multi-sheave block and tackle system, distinct from that of the main-sheet, connected between the main-boom and a relatively fixed part of the vessel, generally the main-mast. As with the block and tackle system of the main-sheet, the block and tackle system of the kicking strap is, invariably, such as to provide a substantial mechanical advantage, 5:1, say, enabling quite large downwardly acting forces to be exerted on the main-boom in response to manual effort applied to the vang block and tackle system. By this means, the leech of the sail may be held adequately taut, the sail being thereby constrained to adopt a satisfactorily relatively flat three-dimensional aerodynamic shape, conducive to good handling of the yacht.
More recently, resort has been had to the employment, as vangs, of gas pressurized spring struts settable to any desired length within a certain range.
The known gas pressurized spring strut vang comprises: a gas pressurized spring device, being a pneumatic or oleo-pneumatic piston and cylinder arrangement the cylinder of which holds a charge of gas, commonly nitrogen, under a high pressure; and, mechanically coupling the piston and cylinder, a multi-sheave block and tackle system offering, as before, a substantial mechanical advantage.
In operation, such a gas pressurized spring strut is suitably pivotally coupled, at one end, to the main-boom and at the other to a part, commonly the main-mast, fixed with respect to the main-boom, and, the tendency of the gas spring device being to expand under the pressure within, the length of the strut is adjusted to the desired length so as to control the tension in the sail, particularly the leech, thereof, by increasing or, as the case may demand, decreasing the length of the multi-sheave block and tackle system by which the piston and cylinder of the strut are coupled.
In order to maintain the length of the block and tackle system at the desired length, the sheet by which the block and tackle system is manually adjusted in length must, the desired length for the strut having been achieved, be secured, as by being trapped in a cleat or other similar device fixed with respect to the hull of the vessel.
It is known, also, to provide a vang constituted as an hydraulically operable, variable length strut, being a strut self-sustaining in length at any desired setting.
Since, for the purpose of contraction, such a strut does not rely on the application of an externally applied manual force, the need for a block and tackle system is avoided.